This invention relates to a plasma processing apparatus, or in particular to a plasma processing method and apparatus suitable for surface treatment of a semiconductor element using the plasma.
It is important to control the temperature of a wafer as a material to be processed (hereinafter referred to as the object material) in the fabrication process of a semiconductor device. As a means to solve this problem, a method is known in which a cooling gas is introduced to produce the cooling effect between the wafer and a substrate electrode, which has an electrostatic chucking film and supports the wafer (JP-A-11-274141).
Also, in the case where the etching process is executed using the plasma processing apparatus, the processing gas is ionized and activated to increase the processing rate and the high-frequency bias power is supplied to the object material in order to cause the ions to enter the object material perpendicularly. In this way, the etching process of high accuracy for an anisotropic shape is realized. Generally, ions enter the object material by being accelerated by the self-bias potential generated by the high-frequency bias power supplied to the object material. By increasing the high-frequency bias power applied to the object material and by thus increasing the self-bias potential, therefore, high-energy ions can be applied to the object material.
As described above, the wafer is mounted on the substrate electrode through the electrostatic chucking film, and a DC voltage is applied to the substrate electrode to chuck the wafer electrostatically. The electrostatic chucking film, therefore, is applied with a voltage corresponding to the difference between the self-bias potential of the wafer and the DC voltage applied to the substrate electrode. In connection with this, a method is known in which the high-frequency voltage of the substrate electrode is monitored, and a predetermined voltage is applied to the electrostatic chucking film (U.S. Pat. No. 6,198,616).
Also, a method is known in which the self-bias voltage of the semiconductor wafer is monitored, the difference between the DC voltage for electrostatic chucking (hereinafter referred to as the electrostatic chucking DC voltage) and the self-bias voltage is calculated, and the electrostatic chucking DC voltage is controlled to secure a constant absolute value of the voltage difference (JP-A-8-124913).